Spin Hall Effect And Magnetic Proximity Effect In YIG/Pt Bilayers

The field of Spintronics explores the strong coupling between spin and charge,which is an important branch of condensed matter physics.The key to this field is to research the generation,manipulation and detection of spin current.As early as 1881,Hall discovered anomalous Hall effect that originated from the spin-orbit coupling between current and magnetic moment in magnetic metal materials.Soon afterwards,magnetic proximity effect was discovered.At the interface between non-magnetic material and ferromagnetic or anti-ferromagnetic material,the interface electrons of non-magnetic materials are spin-polarized due to the exchange interaction of interface electrons.Furthermore,anomalous Hall effect was applied to the experimental research of ferromagnetic/non-magnetic bilayer structures.Borrowing from the concept of anomalous Hall effect,spin Hall effect and inverse spin Hall effect was discovered and widely used as the generator and detector of spin current at the materials with strong spin-orbit coupling.Based on spin Hall effect and interface spin scattering,the concept of spin Hall magnetoresistance was proposed,and it was believed that the magnetoresistance in ferromagnetic/non-magnetic bilayer structure was due to spin Hall effect and inverse spin Hall effect,rather than magnetic proximity effect at the interface.And the magnetoresistance still existed by inserting another non-magnetic layer between bilayer structure,thus refuting the argument of magnetic proximity effect.Therefore,spin Hall effect and magnetic proximity effect at the interface of ferromagnetic/nonmagnetic material have always been hot research topics.Novel metal platinum(Pt)has strong spin-orbit coupling,which can convert spin current into a charge current or vice versa.The platinum films can be used to detect the spin current or drive precessing even fliping magnetizations in ferromagnetic material(FM)/Pt bilayer structures.Their electrical conductivity and magnetic properties will be concealed by the properties of ferromagnetic metals when platinum thin films deposited on thick ferromagnetic metals.Compared with ferromagnetic metal,there is no charge movement in a ferromagnetic insulator,the conductivity of the platinum film deposited on an insulator can be obtained by transport measurement,and the magnetic properties of this platinum film can be studied by the magnetic transport properties of the ferromagnetic insulator.Yttrium iron garnet(Y3Fe5O12,YIG),a ferromagnetic insulator,is often used to prepare FM/Pt bilayer structure,which has the characteristics of low damping,weak ferromagnetism and negligible magnetic anisotropy.Therefore,the FM/Pt bilayer structure has been widely concerned for the past decade.In addition to spin Hall effect based on the spin-orbit coupling,a thin Pt films on a ferromagnetic material(FM)shows ferromagnetic characteristics due to the magnetic proximity effect and thus exists anomalous Hall effect.Both spin Hall effect and magnetic proximity effect are involved in the spin current diffusion process at the interface of an FM/Pt bilayer,and which effect exists has always been controversial.In this work,we fabricated a serial of YIG/Pt bilayers with different Pt thickness and experimentally measured spin Hall magnetoresistance(SMR)caused by spin Hall effect and interface spin scattering,and anomalous Hall resistance(AHR)induced by the interface proximity effect.We proved that both spin Hall effect and magnetic proximity effect exist in YIG/Pt bilayers simultaneously.By comparing to the results measured in reference samples of SiO2/Pt bilayers,we systematically analyzed that these two effects have different influence on spin diffusion,which is essentially important in designing spintronic devices.